Does Work Depend on the Displacement of an Object?

[cp255]

Homework Statement

For which process does the system absorb energy in the form of work?
a) Water Evaporates into steam.
b)Air is compressed by a bicycle pump.
c) Both

Homework Equations

The Attempt at a Solution

I though the answer was both. However, the key says the correct answer was just B. Why would it not be A as well? I thought evaporation required the input of energy.

 

[mfb]

Work is a specific form of energy. While (a) needs energy, it will not use work.

 

[cp255]

I was thinking that maybe although the energy went into the steam they system is the water which would have cooled.

 

[mfb]

Usually the water will cool down, indeed.

 

[cp255]

So what exactly is work then?

 

[mfb]

Work
A force acting over some displacement. There is no such force or displacement involved in evaporation.

 

[Qube]

So what exactly is work then?

Force applied over some unit of distance. If you push against a car and it moves, you've done work.

If you push on a wall, and the wall doesn't move or fall over, then you've done no work. The displacement of the wall here is 0. Now if the wall does fall over then you've done work. Good work!

(Or bad)